(1) Field of the Invention
The invention relates to subsea mats used to protect underwater structures from detrimental physical forces, and cathodic protection systems used to protect underwater structures from detrimental electrical forces.
(2) Description of the Related Art
Various types of subsea mats exist for protecting subsea pipelines. These are disclosed in at least the following patents:
PatentTitle6,416,253Abrasive resistant open cell articulated seabed mat6,106,194Placement device for underwater mats and method6,027,285Mat installation5,975,796Vertical flow diversion mat system5,944,449Non-Abrasive subsea mat5,846,023Non-abrasive subsea mat5,722,795Non-abrasive subsea matNone of these patents disclose active cathodic protection using anodes. Various systems for corrosion protection of subsea structures exist. These are disclosed in at least the following patents:
PatentTitle6,835,291Anode monitoring and subsea pipeline power transmission6,788,075Anode monitoring6,726,831Corrosion protection of electrically heated pipe-in-pipe subseapipeline6,461,082Anode system and method for offshore cathodic protection6,315,497Joint for applying current across a pipe-in-pipe system6,264,401Method for enhancing the flow of heavy crudes throughsubsea pipelines6,179,523Method for pipeline installation6,171,025Method for pipeline leak detection6,142,707Direct electric pipeline heating5,458,441Pipe section for installation into a subsea pipeline5,289,561Subsea pipeline system with electrically heated flexiblepipeline4,705,331Subsea connecting apparatus
U.S. Pat. No. 6,461,082, listed above, discloses a long pipe (“anode carrier”) with conventional anodes attached along its topside. This invention, however, requires additional supporting structure on the ocean floor for the pipe: “The anode carrier is therefore preferably placed on some type of support system, such as a ‘mud mat’ or other latticework, or some type of pipe rack, to prevent the pipe from sinking into the mud.” (Column 4, lines 55-58) This “anode carrier” pipe most likely also needs stabilization mats. U.S. Pat. Nos. 4,484,839 and 4,484,840 disclose anode piles. The use of anode piles requires pile guides, to physically hold the anode piles against the platform. Not all platforms have existing pile guides that are available for this use.
U.S. Pat. No. 4,609,307 discloses anode sleds. The anodes are attached to sleds or pods that are placed on the ocean bottom and electrically connected to the structure or pipeline. However, fabrication and installation practices place practical limitations on the physical size of the sleds. This size restriction limits the number of anodes that can be attached and the spacing of anodes on the sled. When anodes are placed too close to each other on the sled, the anodes will start to electrically interfere with each other, thereby limiting the amount of electrical current that each sled can produce. On a large, deepwater structure, many sleds may be required to produce the desired amount of electrical current. The physical space around the structure available for such use may limit the number of sleds that can be installed, hence making this approach impractical.